Sea walls, river and canal banks, harbour walls and walls surrounding marinas are revetments which pose technical problems not found in dry land embankments e.g. highway embankments and other civil engineering works. "Wet" revetments are subject to the scouring action of flowing water and to direct wave action which can result in severe forces being imposed. Additionally, when constructing a "wet" revetment, the conditions can be difficult. For example the bed on which the revetment must be built can be uneven and levelling it may be an impossible task. Hence, the choice in certain circumstances of broken rock which drops into the crevices and serves to level the bed. Furthermore it may not be possible to use cofferdams to hold back the water and enable building to take place in relatively dry conditions. In these circumstances the lower part of the revetment may have to be constructed underwater. If the water is turbid the first part of the construction must be done "blind" unless the circumstances are such that divers can be used.
"Wet" revetments comprising broken rock, concrete and stone blocks and cast in situ walls are all in common use.
One specific form of revetment block is disclosed in U.S. Pat. No. 3,282,054. This block has a main body portion which is rectangular and a protrusion of T-shape extending from the rear of the body portion. The blocks are arranged in courses. The body portions form the face of the embankment and each body portion rests on the protrusions of the blocks below. The protrusions are buried in the material which forms the embankment. Such a unit can only successfully be used where there is a flat base onto which the lower course is placed. If there is only an uneven base then the block cannot be used successfully. The ability to build horizontal courses is a prerequisite to the successful use of this block. Hence it has no function in underwater work where a rough bed must be built on.